Figure 1- Example of OCC promising services (a) OCC vehicular use case. (b) OCC indoor use case
- OCC: Optical Camera Communication
- VLC: Visible Light Communication
- LiFi: Light Fidelity
- OWC: Optical Wireless Communication
What is Optical Camera Communication?
OCC aims to deliver data from the light source(s) to the camera. Artificial lights (LED light) are available everywhere human being live, and cameras too. The existing infrastructure shall be an advantage of OCC for the market acceptance. As an example shown in Figure 1, promising services of OCC include vehicular OCC (the killer app of OCC), screen signage, and indoor light service.
OCC is different from VLC and LiFi because of various types of receivers being used. Although there seems to be no universally agreed definition of the VLC, this first terminology has described the equipment of communication into illumination devices such as LED light bulbs. The IEEE 802.15.7-2011 standard is well known as the VLC specification. After the release of the VLC specification, the development of LiFi became even more advanced. LiFi is a common terminology for bidirectional high-speed VLC and networked wireless communications. Because all three OWC technologies (OCC, VLC, and LiFi) rely on optical wavelengths, they do not interfere with RF. IEEE 802.15.7m OWC complements any of the IEEE 802.11 RF technologies, including 802.11p Wireless Access for the Vehicular Environment and Wi-Fi. (//My comment: We might think more about light pollution shortly rather than the technical feasibility concerns).
In VLC and LiFi systems, PD is used just to receive data. Conversely, in OCC systems, the communication function of cameras is supplementary to their primary function that is to capture images. Without any need of modifying hardware to assist the communication purpose, a typical camera consisting of a lens and two-dimensional image sensor is beneficial to the communication due to the spatial separation of light from its existent lens in comparison with PD. In conjunction with a high image resolution, the camera can demodulate multiple light sources that are spatially separated simultaneously. Despite these significant advantages of cameras, camera-based OWC has only recently been adopted in the ongoing OWC standardization at IEEE 802.15.7m Task Group (TG7m).
OCC Receiver Types?
The choice of camera receiver affects the selection of signal formats transmitted by the LEDs. Notably, the type of camera limits the OCC performance. Thus, cameras must be classified by the effects of their characteristics on the communication performance, as described below.
The frame rate is the primary determiner of signal acquisition by the camera. For a single LED light source in Tx, the frequency of sampling of a camera Rx determines how much data can be demodulated, following Nyquist sampling theory. Smartphone cameras typically operate at a low frame rate such as 30 frame-per-second (fps), whereas specific cameras may reach rates of 1000 fps or higher.
The shutter mechanism determines the exposure of the pixels in an image. Based on their shutter mechanism, cameras can be classified into global or rolling shutter classes. Rolling shutter cameras, which sequentially expose pixel rows to light, must sample quickly enough to detect the changing light intensity modulated in the rolling image. Global shutter cameras, which expose all pixels simultaneously, require a sufficiently fast frame rate to detect the change of light intensity of each LED over consecutive images.
Classification of OCC Technologies
Various modulation schemes for OCC systems have been investigated till the date. The selected modulation scheme depends on both Tx and Rx. Table 1 classifies OCC schemes into four categories under the following considerations:
(i) The method by which the camera Rx samples the modulated light signal. The type of camera acquiring the data is critical to the communication, so the communication system is limited by the camera specifications rather than Tx.
(ii) The characteristics of the modulated light as perceived by the human eye. The light sources and their modulation must be selected appropriately because the primary purpose of a light source is illumination, whereas communication is the secondary concern.
Table 1 – Characteristics and Performance Estimation of OCC Technologies